The highly disordered C-terminal tail (CH1) of Histone H1 condenses internucleosomal linker DNA in chromatin in a way that is still poorly understood. Moreover, CH1 is phosphorylated in a cell cycle-dependent manner that correlates with changes in the chromatin condensation level. In S phase, phosphorylation correlates with a more open chromatin structure that would facilitate replication and transcription and, in M phase, probably enables rearrangement of the condensed chromatin structure (e.g., to allow entry of condensins). The chromatin-condensing properties of H1 are mainly conferred by its ca. 100-residue-long polycationic C-terminal tail, CH1. In chromatin, the tail, which contains several phosphorylation sites, interacts with and condenses internucleosomal linker DNA CH1 remains disordered in the DNA-bound state, despite its nanomolar affinity. Phase-separated droplets (coacervates) form, containing higher-order assemblies of CH1/DNA complexes. Phase-separated condensates form, containing higher-order structures that are highly sensitive to the phosphorylation state of H1, suggesting a mechanism by which condensation of the chromatin fiber and other assemblies might be regulated (PMID:30301810).